Offset blade tip chord sealing system and method for rotary machines

ABSTRACT

A rotary machine includes a rotary member disposed inside the stationary member, wherein the rotary member includes at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls. A sealing system is disposed on the tip portion. The sealing system consists essentially of at least one seal strip disposed on the tip portion at an off-center position only between the downstream side wall and a central position between the upstream and downstream sidewalls.

BACKGROUND

The invention relates generally to a rotary machine and, more particularly, a sealing system for an interface between rotating and stationary components. In certain aspects, the sealing system includes a sealing system between a rotating blade and a surrounding structure of a turbine engine.

Performance and efficiency of rotary machines, e.g., turbine engines, are dependent on a clearance gap between rotating and stationary components within the turbine engine. For example, the clearance gap between the tip of rotor blades and the adjacent stationary shrouds provides a narrow flow passage between the pressure and suction sides of the rotor blade, resulting in hot gas flow leakage that can reduce the blade aerodynamic performance. As the clearance gap between the rotating and the stationary components increases, the efficiency of the turbine decreases. In addition, the hot gas flow leakage in the area of the blade tip can increase thermal loading on the rotor blade.

Several blade tip designs exist for maintaining proper pressure between the pressure side and the suction side flow surfaces of the rotor blade as well as for providing minimum clearances with the stator shroud. Existing blade tip treatments for sealing have cost implications, involving additional amounts of material to form the tip treatment for sealing. Moreover, existing blade tip designs lead to re-attachment of fluid flow at the blade tip surface causing increased tip heat load at the tip surface.

BRIEF DESCRIPTION

In accordance with one aspect of the present invention, a rotary machine includes a rotary member disposed inside the stationary member, wherein the rotary member includes at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls. A sealing system is disposed on the tip portion. The sealing system consists essentially of at least one seal strip disposed on the tip portion at an off-center position substantially between the downstream side wall and a central position between the upstream and downstream sidewalls.

In accordance with another aspect of the present invention, a turbine includes a rotor disposed inside the stationary outer casing, wherein the rotor comprises at least one rotor blade having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls. At least one seal strip is disposed on the tip portion at an off-center position substantially between the downstream side wall, and a central position between the upstream and downstream side walls.

In accordance with another aspect of the present invention, a sealing system includes at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls. At least one seal strip is disposed on the tip portion at an off-center position only between the downstream side wall and a central position between the upstream and downstream side walls.

In accordance with another aspect of the present invention, a method includes rotating a rotary member having at least one airfoil disposed inside a stationary member. A flow resistance to the flow of the working fluid between a tip portion of the airfoil and the stationary member is created via at least one seal strip disposed on the tip portion at an off-center position only between a downstream side wall and a central position between an upstream side wall and the downstream side wall of the airfoil. Leakage of flow of a working fluid between the rotary member and stationary member is reduced.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical view of a rotary machine, e.g., gas turbine engine system, having an offset blade tip chord sealing system in accordance with an exemplary embodiment of the present invention;

FIG. 2 is a diagrammatical view of an offset blade tip chord sealing system for a rotary machine as illustrated in FIG. 1 in accordance with an exemplary embodiment of the present invention;

FIGS. 3-6 are diagrammatical views of an offset blade tip chord sealing system for a rotary machine in accordance with various embodiments of the present invention;

FIG. 7 is a graph representing variation between blade tip averaged heat transfer with respect to percentage axial chord in accordance with certain embodiments of the present invention; and

FIG. 8 is a flow chart illustrating exemplary steps involved in a method of operating a rotary machine in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

As discussed in detail below, embodiments of the present invention provide a rotary machine in which an offset blade tip chord sealing system is disposed on a tip portion of at least one airfoil of a rotary member. In accordance with some embodiments of the present invention, the sealing system includes one or more seal strips (e.g., a single strip) disposed on the tip portion only at a substantially or generally off-center position between a downstream side wall and a central position between the downstream side wall and an upstream side wall of the airfoil, for example, a seal strip at or near the downstream side wall. In other words, at least a substantial portion, or most, or all of the one or more seal strips may extend along the tip portion between the central position and the downstream side wall. Thus, the sealing system may exclude seal strips disposed on the tip portion entirely or mostly between the central position and the upstream side wall, for example, a seal strip at or near the upstream side wall. The exemplary sealing system is configured to maintain minimal clearances between the rotary member and a surrounding stationary member resulting in reduced fluid leakage and increased efficiency of the rotary machine. The sealing system also facilitates usage of less exposed material on the tip portion of the airfoil to provide a tip load heat reduction since a seal strip (e.g., a single strip) is disposed on the tip portion only at an off-center position between the downstream side wall and the central position between the downstream side wall and the upstream side wall of the airfoil. Specific embodiments of the present invention are discussed below referring generally to FIGS. 1-9.

Referring to FIG. 1, an exemplary rotary machine, such as a turbine assembly 10, is illustrated in accordance with aspects of the present invention. The turbine assembly 10 includes a plurality of rotary members or rotors 12 and a stationary member 14, such as a stationary outer casing, concentrically disposed about the rotary members 12. As discussed below, the turbine assembly 10 includes an offset blade tip chord sealing system 32 between the rotary and stationary members 12 and 14. Each rotary member 12 includes an inner base portion 16, an airfoil or rotor blade 18, and an outer tip portion 20. Although the aspects of the present invention are described herein with respect to turbine assembly 10, in certain other exemplary embodiments the sealing system may be used in other rotary machines in which leakage of working fluid is a concern. For example, exemplary rotary machines may include compressors, pumps, motors, or the like. Moreover, exemplary systems utilizing these rotary machines may include power generation systems, for example, industrial machine, watercraft, aircraft, and other vehicles. In the illustrated embodiment, the turbine assembly 10 may further include a steam turbine or a gas turbine. Moreover, the turbine assembly 10 may include a compressor coupled to a turbine via a shaft, one or more gas turbine combustors disposed between the compressor and the turbine, a fuel injection system coupled to the one or more gas turbine combustors, and so forth.

The airfoil 18 extends outwardly into a working fluid flow path of the turbine assembly 10 where the working medium gases exert motive forces on a plurality of surfaces thereof. The airfoil 18 includes an upstream sidewall 22 and an opposite downstream side wall 24 (see FIG. 2) joined together at a leading edge 26 and a trailing edge 28. The stationary member 14 is spaced apart from the tip portion 20 so as to define a clearance gap 30 therebetween. The performance and efficiency of the turbine assembly 10 is affected by the clearance gap 30. As the amount of leakage flow through the clearance gap increases, the efficiency of the turbine is reduced, since the leakage flow does not exert motive forces on the airfoil surfaces and accordingly does not provide work. The offset blade tip chord sealing system 32 is disposed on the tip portion 20 of the airfoil 18 and configured to reduce leakage of fluid along the tip portion 20 from the upstream side to the downstream side of the airfoil 18, while also reducing the heat load on a tip surface of the airfoil. The sealing system 32 is explained in greater detail with respect to subsequent figures.

Referring to FIG. 2, the offset blade tip chord sealing system 32 is illustrated in accordance with certain embodiments of the present invention. In the illustrated embodiment, the tip portion 20 is defined by the upstream side wall 22, the downstream side wall 24, the leading edge 26, and the trailing edge 28. The tip portion 20 also comprises a tip surface 34. The direction of rotation of the airfoil 18 is represented by the arrow 36. The sealing system 32 is disposed on the tip surface 34. The sealing system 32 includes a seal strip 38 disposed on the tip surface 34 only at a generally off-center position between the downstream side wall 24 and a central position 40 between the upstream side wall 22 and the downstream side wall 24. For example, the seal strip 38 may extend along the downstream side wall 24 at a slight offset near the downstream side wall 24. In addition, the seal strip 38 is at least substantially or mostly between the central position 40 and the downstream side wall 24, although some portion of the seal strip 38 may be positioned across the central position 40. However, the sealing system 32 generally excludes any seal strips extending along the upstream side wall 22 at a position near or directly at the upstream side wall 22. Moreover, the sealing system 32 generally excludes any seal strips disposed between the upstream side wall 22 and the central position 40. Again, the sealing system 32 may include some portion of the seal strip 38 extending across the central position 40 toward the upstream side wall 22, while at least a substantial portion or most of the seal strip 38 remains positioned between the central position 40 and the downstream side wall 24.

In one embodiment, the entire seal strip 38 is disposed on the tip surface 34 only at a generally off-center position between the downstream side wall 24 and a central line 41 extending between the leading edge 26 and the trailing edge 28. In another embodiment, a substantial portion of the seal strip 38 is positioned between the central line 41 and the downstream side wall 24, while either ends 43,45 of the seal strip 38 extend across the central line 42 towards the upstream side wall 22.

In certain embodiments, the sealing system 32 may further include one or more additional seal strips between the central position 40 and the downstream side wall 24. The seal strip 38 enhances the flow resistance through the clearance gap 30 and thus reduces the flow of hot leakage gas for a predetermined pressure differential so as to improve the overall turbine efficiency. The width and height of the seal strip 38 may be varied for better performance, typically depending upon the size of the overall turbine assembly. Examples of configurations of the seal strip are illustrated in subsequent figures.

The offset of the seal strip 38 inward from the downstream side wall 24 creates a step 42 along the downstream side wall 24. The leakage flow is directed along the tip portion 20 from the upstream side to the downstream side of the airfoil in such a way that the fluid flows over the seal strip 38 to the recessed portion between the protruded seal strip 38 and the downstream side wall 24) that contains a separated flow region (low heat transfer region) at the downstream side. Additionally, the seal strip 38 also serves as a flow resistance element. The offset of the seal strip 38 from the downstream side wall 24 may also be varied for better performance, depending upon the size of the turbine assembly.

The offset of the seal strip 38 from the downstream side wall 24 also serves to reduce the tip cavity width to depth ratio, thereby providing lower cavity floor heat transfer. The seal strip 38 may also include at least one slot 44 proximate to the trailing edge 28 for exiting any tip cavity coolant flow. In other words, the seal strip 38 may include a series of sequential strips or longitudinally aligned strips, rather than a single continuous strip. Location, size, and orientation of the slot 44 may be varied depending upon the requirement. In accordance with aspects of the present invention, the seal strip 38 is located on the tip portion 20 in such a way so as to receive a cooling flow from the internal cooling passages of the airfoil 18. The seal strip 38 may be formed, for example, by integral casting with the airfoil tip portion, by electron-beam welding of flow discouragers to the airfoil tip portion, by physical vapor deposition of material to the airfoil tip portion, or by brazing, or a combination thereof. Alternately, the airfoil tip portion which has been cast to oversized dimensions, may have material removed by various methods, for example laser ablation, or the like, thereby forming the seal strip. In certain embodiments, the provision of the seal strip 38 only proximate the downstream side wall 24 of the tip portion 20 of the airfoil 18 reduces the amount of material used for tip treatment of an airfoil for sealing. Moreover, the seal strip 38 reduces the likelihood for cracking of the tip portion of the airfoil.

Referring to FIG. 3, a diagrammatical sectional view of the offset blade tip chord sealing system 32 is illustrated in accordance with certain embodiments of the present invention. The stationary member 14 is spaced apart from the tip portion 20 so as to define the clearance gap 30 therebetween. As discussed above, the offset blade tip chord sealing system 32 is disposed on the tip portion 20 of the airfoil 18 and configured to reduce leakage of fluid along the tip portion 20 from the upstream side to the downstream side of the airfoil 18, while also reducing the heat load on a tip surface of the airfoil. In certain embodiments, width “W” of the seal strip 38 ranges from about 0.015 to about 0.040 inches for aero engines, and about 0.050 to about 0.125 inches for heavy frame turbines. In certain embodiments, seal height “H” ranges from about 0.060 to about 0.125 inches for aero engines, and about 0.150 to about 0.250 inches for heavy frame turbines. In certain embodiments, seal offset “D” is at least equal to a radius of curvature “R” of a tip edge of the airfoil 18, or a wall thickness “T” of the airfoil. In certain exemplary embodiments, the seal offset “D” is less than or equal to about 4 times the seal height “H”. In certain other exemplary embodiments, the wall thickness “T” is in the range of about 0.020 to about 0.040 inches for aero engines, and about 0.040 to about 0.150 inches for heavy frame turbines.

Referring to FIG. 4, a diagrammatical sectional view of the offset blade tip chord sealing system 32 is illustrated in accordance with certain embodiments of the present invention. The offset blade tip chord sealing system 32 is disposed on the tip portion 20 of the airfoil 18 and configured to reduce leakage of fluid along the tip portion 20 from the upstream side wall 22 to the downstream side wall 24 of the airfoil 18, while also reducing the heat load on a tip surface of the airfoil 18. In the illustrated exemplary embodiment, radius of curvature “R” of a tip edge of the airfoil 18 is equal to zero. In other words, the tip edge at the upstream and downstream side walls 22 and 24 is not curved, but rather has a sharp or 90 degree edge. In the illustrated embodiment, seal offset “D” is at least equal to a wall thickness “T” of the airfoil. In certain exemplary embodiments, the seal offset “D” is less than or equal to about 4 times the seal height “H”. In one exemplary embodiment, the seal offset “D” is equal to about 2 times the seal height “H”.

Referring to FIG. 5, a diagrammatical sectional view of the offset blade tip chord sealing system 32 is illustrated in accordance with certain embodiments of the present invention. The offset blade tip chord sealing system 32 is disposed on the tip portion 20 of the airfoil 18 and configured to reduce leakage of fluid along the tip portion 20 from the upstream side wall 22 to the downstream side wall 24 of the airfoil 18, while also reducing the heat load on the tip surface of the airfoil 18. In the illustrated embodiment, the seal strip 38 has a base portion 46 having fillets. In other words, the seal strip 38 gradually curves outwardly in a downward direction onto the tip portion 20. The provision of base portion 46 having fillets enhances creation of a separation zone for leakage fluid with lower heat transfer and also placement of the seal feature over an internally cooled region of the airfoil tip portion 20.

Referring to FIG. 6, a diagrammatical sectional view of the offset blade tip chord sealing system 32 is illustrated in accordance with certain embodiments of the present invention. The offset blade tip chord sealing system 32 is disposed on the tip portion 20 of the airfoil 18. In the illustrated embodiment, the seal strip 38 has a rounded top portion 48. In certain embodiments, the illustrated sealing system 32 reduces the likelihood or amount of leakage of working fluid along the tip portion 20 from an upstream side wall 22 to a downstream side wall 24 of the airfoil 18, while also reducing the heat load on the tip surface of the airfoil 18.

Referring to FIG. 7, a graph representing variation of airfoil tip averaged heat transfer (y-axis) represented by reference numeral 50 versus percentage axial chord of the airfoil (x-axis) represented by reference numeral 52 is illustrated. Axial chord refers to the length from the leading edge 26 to the trailing edge 28 of the tip portion 20 of the airfoil 18 as represented in FIG. 2. Curves 54, 56, and 58 represent variation of airfoil tip averaged heat transfer with respect to percentage axial chord for a 40 mils squealer seal strip, a 100 mils squealer seal strip, and a 40 mils seal strip disposed on the tip portion only at an off-center position between the downstream side wall and the central position between the downstream side wall and the upstream side wall, respectively of the airfoil. The squealer seal strips are located along the entire outer periphery of the tip portion of the airfoil. With respect to curves 54, 56, and 58, the airfoil tip averaged heat transfer decreases gradually from the leading edge up to a predetermined point and then increases gradually towards the trailing edge of the tip portion of the airfoil. The tip averaged heat transfer for the 100 mils squealer seal strip and the 40 mils seal strip disposed on the tip portion at an off-center position between the downstream side wall and the central position between the downstream side wall and the upstream side wall, relative to percentage axial chord is comparatively less than the tip averaged heat transfer for 40 mils squealer seal strip. As illustrated by the curves 54, 56, and 58, the tip averaged heat transfer decreases from the leading edge to the trailing edge upto a predetermined point, and then increases gradually towards the trailing edge. The tip averaged heat transfer of tip portion of the 40 mils seal strip disposed on the tip portion only at an off-center position between the downstream side wall and the central position between the downstream side wall and the upstream side wall of the airfoil, is less compared to that of the 40 mils squealer seal strip, and the 100 mils squealer seal strip.

Referring to FIG. 8, a flow chart illustrating exemplary steps involved in method of operating a rotary machine is illustrated. In accordance with the illustrated exemplary embodiment, the method includes rotating the rotary member disposed inside the stationary member as represented by step 60. For example, as illustrated in FIG. 1, the method involves rotating the rotor disposed inside the stationary outer casing. During operation of the machine, the tip portion of the airfoil is internally cooled as represented by step 62. The tip portion allows cooling flow to be released from the interior of the blade through holes (not illustrated) in the tip portion of the airfoil. In accordance with certain embodiments, the seal strip is located directly over the internally cooled portion of the tip portion of the airfoil.

The sealing system includes the seal strip disposed on the tip surface only at an off-center position between the downstream side wall and a central position between the upstream side wall and the downstream side wall. The seal strip enhances the flow resistance of leakage fluid through the clearance gap between the tip portion of the airfoil and the stationary member as represented by step 64. The offset blade tip chord sealing system disposed on the tip portion of the airfoil also reduces leakage of fluid along the tip portion from the upstream side to the downstream side of the airfoil for a predetermined pressure differential so as to improve the overall turbine efficiency as represented by step 66.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. 

1. A rotary machine, comprising: a stationary member; a rotary member disposed inside the stationary member, wherein the rotary member comprises at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls; and a sealing system disposed on the tip portion, wherein the sealing system consists essentially of: at least one seal strip disposed on the tip portion at an off-center position substantially between the downstream side wall and a central position between the upstream and downstream sidewalls.
 2. The machine of claim 1, wherein the rotary machine comprises a turbine.
 3. The machine of claim 1, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a wall thickness of the at least one airfoil.
 4. The machine of claim 1, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a radius of curvature of a tip edge of the at least one airfoil.
 5. The machine of claim 1, wherein the at least one seal strip includes a first portion positioned between the downstream side wall and the central position and a second portion disposed between the upstream side wall and the central position, wherein the first portion is substantially greater than the second portion.
 6. The machine of claim 1, wherein the seal strip comprises a base portion having fillets.
 7. The machine of claim 1, wherein the seal strip comprises a rounded top portion.
 8. A turbine, comprising: a stationary outer casing; a rotor disposed inside the stationary outer casing, wherein the rotor comprises at least one rotor blade having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls; and at least one seal strip disposed on the tip portion at an off-center position substantially between the downstream side wall, and a central position between the upstream and downstream side walls.
 9. The turbine of claim 8, wherein a width of the at least one seal strip is in range of 0.05 to 0.125 inches.
 10. The turbine of claim 8, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a wall thickness of the at least one rotor blade.
 11. The turbine of claim 8, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a radius of curvature of a tip edge of the at least one rotor blade.
 12. The turbine of claim 8, wherein a height of the at least one seal strip is in the range of 0.150 to 0.250 inches.
 13. The turbine of claim 12, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall equal to twice the height of the at least one seal strip.
 14. The turbine of claim 8, wherein the at least one seal strip comprises a base portion having fillets.
 15. The turbine of claim 8, wherein the at least one seal strip comprises a rounded top portion.
 16. A sealing system, comprising: at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls; and at least one seal strip disposed on the tip portion at an off-center position only between the downstream side wall and a central position between the upstream and downstream side walls.
 17. The sealing system of claim 16, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a wall thickness of the at least one airfoil.
 18. The sealing system of claim 16, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a radius of curvature of a tip edge of the at least one airfoil.
 19. The sealing system of claim 16, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall equal to twice the height of the at least one seal strip.
 20. The sealing system of claim 16, wherein the at least one seal strip comprises a base portion having fillets.
 21. The sealing system of claim 16, wherein the at least one seal strip comprises a rounded top portion.
 22. A method, comprising: rotating a rotary member having at least one airfoil disposed inside a stationary member; and reducing leakage of flow of a working fluid between the rotary member and stationary member, comprising: creating a flow resistance to the flow of the working fluid between a tip portion of the airfoil and the stationary member via at least one seal strip disposed on the tip portion at an off-center position only between a downstream side wall and a central position between an upstream side wall and the downstream side wall of the airfoil.
 23. The method of claim 22, further comprising internally cooling the tip portion of the airfoil.
 24. The method of 22, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a wall thickness of the at least one airfoil.
 25. The method of 22, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a radius of curvature of a tip edge of the at least one airfoil.
 26. The method of 22, wherein the at least one seal strip comprises a base portion having fillets.
 27. The method of 22, wherein the at least one seal strip comprises a rounded top portion. 